ABSTRACT
Phosphorus
is an essential nutrient for plant growth but in excess is a source of environmental
pollution. Fertilizer additions of P are recommended based on soil tests;
however, the commonly applied P extractants are often applied outside of their
design criteria (specifically soil pH). As a result, soil tests can produce
inaccurate estimates of plant available P in the soil, which either increases P
loss in runoff, contributing to eutrophication, or decreases crop production
contributing to economic loss. In this
study, 200 diverse soils from across the US were extracted with Mehlich 3, water,
H3A-3, and FeAlO strips. Comparison with FeAlO was critical, as this method is
accepted as the “gold standard” for plant-available P, but it is rarely used in
commercial labs because of time and financial constraints. H3A-3 produced mean,
median, standard deviations that are very similar to FeAlO strip results and
low relative errors (<10%), as well as highly correlated regression
relationships (r2 > 0.96 with slopes 0.95 - 0.98). Although
Mehlich 3 and water were correlated with FeAlO, Mehlich 3 (strongly acidic)
extracted much more P than FeAlO, and water (low buffering capacity) extracted
much less P across the range of soil pH values. Thus, H3A-3 provides an
improved methodology to accurately determine plant-available P by mimicking
root exudate action in the soil, while avoiding the time-consuming and costly
FeAlO procedure. In the face of high-profile water quality impairments with
enormous economic costs, such advancements are critical to balance agronomic
production with environmental concerns.